In evaporative type air coolers it is desirable that there be a minimum number of metal parts due to danger of corrosion, and there is a need to key a shaft and impeller together so that there is little danger of relative rotational movement due to torsional forces.
If an impeller is formed from polymeric material by an injection moulding process, and the impeller is to be mounted on a circular section shaft it is usually necessary to incorporate a key insert in the hub of the impeller, and this reduces production output of a moulding machine. One object of this invention is to provide improvements wherein an impeller can be moulded entirely as an integral moulding of polymeric material without any metal inserts, and in this invention this is achieved by utilising a square section shaft which is engaged by inner surfaces of the hub of the impeller. If the hub is made of sufficient length the risk of relative rotational movement with respect to the shaft can be so small as to be negligible.
Another problem which is encountered in production is the difficulty of quick and efficient assembly, and in this invention there are provided adaptors near each end of the shaft, each adaptor having internal surfaces lying in face-to-face contiguity with the surfaces of the shaft and having curved external surfaces which support respective bearings.